I am building an L shaped office desk from pipe, structural fittings. The top will be in two pieces cut from a 4x8 sheet of Baltic birch plywood. I'd like the desk, including the top, to be disassemble-able and, if at all possible, for there not to be a leg at the inside corner.

I'm looking for recommendations on joining the two top pieces given the above objectives (includes orientation of joint - see image)

Some thoughts I've had (NB: effectively total noob to this sort of thing)

simply glue it (permanent)

dowel, biscuits, spline (permanent, complex/hard for me)

apron across the edge with the joint

piece across joint on underside screwed into the top pieces (prob. can't disassemble too many times)

3 Answers
3

Don't mess around with a mitered corner (At best you're just wasting wood with the triangular cut-offs.

Make the top of two rectangles joined with the lap joint(easy) or the dog bones (fun to work out).

Assuming you plan on using flanges to join the legs to the top, overlap one flange so that it attaches to both pieces of the top. Most of the load will be carried by the leg and little load needs to transferred from one piece of the top to the next. The leg labeled as optional is necessary only if you are anticipating heavy loads (e.g. lots of books)

I have seen tables with pipe legs like you plan to use. They have seemed remarkably stable and will hold up quite nicely if not abused - move by lifting, not dragging; it's not a chair so don't sit or dance on it.

The ability to knock down and re-build a piece of furniture is over-rated for the needs of most people. While young, still getting an education, moving every year or two years, it is handy, but in the end, modular furniture is re-assembled at most a handful of times. So, listen to Benchwerks, if the screw holes become too loose, relocate them.

After thought: My experience with Baltic birch has been that it comes in square sheets 60" on a side. You can make your top without piecing together parts.

Appearance-wise, consider the direction of the wood grain at the various joints. You show a 38" x 24" butting to an 18" x 54". If you are using a single piece of plywood you must change the grain direction at the joint, so if appearances are important decide of other joint directions work better.

Material thickness and strength. Your desktop material is thin and dowels or splines may too weak to support weight and/or movement, it depends on how it will be used. A stronger joint option for this application might be to screw/glue attach a second piece of plywood (4"x 24"+/-) to connect the two pieces from below.

The joint location will be the weakest point of the desktop (think of the connection as a hinge location. Interrupting the desktop with a joint in the middle (more or less) of the span is asking for failure unless that joint is adequately supported below.

Connecting legs with flat plates to the underside of the desk will not be stable. See this question for additional thoughts on this problem.

In order to adequately support your desktop you should consider aprons at least 3-4" deep. The inside corner of the desk where you wish to avoid a leg must carry across the entire width of the desk (56") and connect to an apron on the 54" side that is supported by the corner legs. Consider the height of the top, seat and clearance for the persons body when determining the length of your legs.

Given your level of experience, I would choose the "piece across the joint" option. It's been used in the countertop industry for eons. Since you are using Baltic Birch for the top (excellent choice in terms of stability and relative strength) you can glue and clamp everything together. Or not, if you plan on taking it apart - you can always change the location of the screw holes.

Other issues, such as what sort of load this top will carry, require more info. But you got a good start!